Electric machines i.e. electric motors and electric generators are used in many applications. Electric motors are used to drive different kinds of machines and electric generators are used to produce electric power. The power sources used to drive electric generators vary. Steam is one common power source used in electric power plants to drive turbines, whereby the turbines drive the electric generators. Combustion engines can on the other hand be used to drive generators. The combustion engine and the generator are often mounted on a common platform forming a support structure. The whole unit comprising the combustion engine and the electric generator on the common platform can then be transported to the site and positioned on the floor in the power building. The installation of such a unit is thus very fast.
The stator in an electric generator comprises normally an annular stator core and a stator frame surrounding the stator core. The inner surface of the stator core comprises slots opening into the inner surface of the annular stator core. The stator winding is positioned in the slots. There are further back beams extending in the axial direction along the outer surface of the stator core. The back beams are welded to the outer surface of the stator core. The stator frame comprises normally end constructions and frame plates between the end constructions. The stator frame can be manufactured simultaneously with the stator core. The stator frame can then be installed on the stator core when the stator core is ready.
The stator core is in prior art solutions attached to the stator frame by welding. This is done by using C-formed clamps that are positioned on the back beams on the outer surface of the stator core. The C-clamps are then welded to the stator frame and to the stator core. The stator core is first positioned in the correct position in relation to the stator frame before the welding is done.
The stator frame is in prior art solutions attached via support elements to the support structure. The support elements are attached by welding to the stator frame and to the support structure by bolts.
The use of welding for attaching the stator core to the stator frame and for attaching the support elements to the stator frame is, however, problematic especially in generator applications where the generator is driven by a combustion engine. The combustion engine produces heavy vibrates to the common support structure and thereby also to the electric generator. The electric generator will thus work in a constantly vibrating environment. These vibrations will cause a heavy load on the welded joints during the long lifespan of the generator. The number of vibrations that an electric motor is subjected to during its lifetime is in the order of 109. The great number of vibrations is problematic for welded joints, which might at some point brake due to these vibrations. It has in fact been observed that these vibrations have caused braking of the welded joints in some circumstances. The welded joints between the stator frame and the support elements are weak points in the construction as the moment of inertia of the stator is transferred from the stator to the support structure through these joints.
There is thus a need to find a solution to this problem that the welded joints might brake due to vibration.
U.S. Pat. No. 540,199 discloses an electric machine with a rotor and a stator surrounding the rotor. The stator core is formed of sheets that are clamped together with clamping bars extending between end plates of the stator core. Dovetail keys are used that fit into a first groove in the clamping bars and into a second groove in the stator core in order to attach the clamping bars to the stator core. There are nuts at the ends of the clamping bars for pressing the end plates and the sheets in the stator core together. The stator frame is formed of radially extending annular supporting and stiffening plates. There are further axially extending ring formed support parts between the annular supporting and stiffening plates. The outer edges of the annular supporting and stiffening plates are further secured with a wrapper plate. A ring is further welded to the inner edge of at least some of the supporting and stiffening plates. The fastening arrangement between the stator core and the stator frame comprises axially directed longitudinal beam springs extending on the outer surface of the laminated core. The beam springs are arranged in pairs one on each side of a clamping bar. The beam springs have an enlarged portion at both ends and at the axial center of the beam spring. These beam springs are secured at the enlarged portions at both ends with radially directed bolts to a respective ring. The beam springs are further secured at the enlarged portion in the middle of the beam spring with tangentially directed bolts to a respective clamping bar. A spacing block is further provided between each of the beam springs and the adjacent clamping bar to provide a slight clearance between the beam spring and the clamping bar to allow for slight tangential flexing on the beam springs without resulting in contact between the beam springs and the clamping bars.
GB patent application 2470467 discloses a system and method for generator mounting. The stator comprises a stator core and a stator frame. There are axial key bars attached to the outer circumference of the stator core. There are further axial spring bars attached to an inner perimeter of the stator frame. The axial key bars and the axial spring bars are connected with alignment adapters comprising outer and inner recesses disposed radially opposite from each other. The outer recess is configured to hold a spring bar and the inner recess is configured to hold a key bar. The alignment adapter is configured to align the key bar to the stator in a circumferential direction via a circumferential position of the outer recess relative to the inner recess. There are fastening bolts passing through a hole in the spring bar and the adapter to the thread in the key bar. A play has been arranged between the bolt and the hole in order to allow for a slight movement of the relative position between the spring bar and the key bar.